Image processing circuit and image processing method thereof

ABSTRACT

An image processing circuit and an image processing method thereof are disclosed. A difference value adaptor of the image processing circuit produces a weighing value and a flag value corresponding to the pixel according to the pixel difference value of each pixel of an input video signal. The image processing circuit judges which area among a first area, a second area and a third area the pixel difference value of each pixel falls in according to the flag value. The image processing circuit performs a low-pass filtering processing on the pixel having the pixel difference value falling in the first area, performs a high-pass filtering processing on the pixel having the pixel difference value falling in the second area and performs a luminance transient improvement processing (LTI processing) on the pixel having the pixel difference value falling in the third area.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 98116402, filed on May 18, 2009. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an image processing circuitand an image processing method thereof, and more particularly, to animage processing circuit and an image processing method thereof forperforming adaptive processing according to the image characteristic.

2. Description of Related Art

When watching images, a viewer pays attention to not only the color andthe hue of the images, but also to the profiles or the edges of theobjects in the images. The image processing is used to enhance the imagefeatures for improving or increasing the visual effect of the images.For example, images obtained by a digital camera or a scanner usuallyare processed with a post procedure so as to look more clear andrich-colorful.

One of the image processing techniques is sharpening processing, whereinin an image undergone the sharpening processing, the profiles or theedges of the image objects have higher contrast to distinguish the imageobject from others. On the other hand, ‘sharpness’ usually representsthe sharpened extent of an image. For a viewer, an image with highersharpness usually looks more clear than that with lower sharpness.

Although the sharpening processing can gain a higher contrast of theprofiles or the edges of the image objects, but it may cause negativeeffect as well. For an image where the edges of the objects are clearalready, a further sharpening processing may make the edges thereofgenerate unacceptable visual effect such as light contour.

US Patent Application No. 2005/0270425 discloses a video signalprocessing device 100, as shown by FIG. 1. Referring to FIG. 1, a videosignal processing device 100 receives an input video signal S_(A),performs a sharpening processing on the input video signal S_(A) andthen produces an output video signal S_(D). FIGS. 2A-2E are timingcharts of the partial signals in the video signal processing device 100of FIG. 1. Referring to FIG. 2A, the input video signal S_(A) hereinincludes a general video signal S and noises n₁ and n₂, wherein thegeneral video signal S carries the image information. The video signalprocessing device 100 would increase the sharpness of the images in thegeneral video signal S and avoid the noises n₁ and n₂ from beingsharpened.

The video signal processing device 100 includes a signal delayer 101, aweighing unit 103, a first multiplier 109, a second multiplier 111, anadder 113 and a high-pass filter 115. Referring to FIGS. 1 and 2B, thehigh-pass filter 115 receives the input video signal S_(A) and performsa high-pass filtering processing on the input video signal S_(A) so asto produce a high-frequency signal S_(B). The high-frequency signalS_(B) is used as base for judging the profiles/edges of the imageobjects. In more details, the amplitudes of the video signal S arecorresponding to the pixel values of the frame pixels. When theamplitudes of the video signal get varied, it indicates there aredifferences between the pixel values of adjacent pixels in a frame. Inparticular, a larger amplitude variation of the video signal S iscorresponding to the portion of profiles/edges of the image objects inthe frame, so that the high-pass filter 115 would filter out thecomponent with larger amplitude variation to produce the high-frequencysignal S_(B). As a result, the produced high-frequency signal S_(B)would be used as base by the video signal processing device 100 forsharpening processing.

Referring to FIGS. 1 and 2C, the weighing unit 103 includes an edgecalculator 105 and a weight calculator 107. The edge calculator 105receives the input video signal S_(A), detects the image information inthe input video signal S_(A) and calculates the pixel differencesbetween the present pixel and the adjacent pixels thereof so as to judgewhich area the present pixel belongs to. After that, the weightcalculator 107 accordingly produces a weighing signal S₁ according tothe judgement result of the edge calculator 105, wherein the weightvalue contained by the weighing signal S₁ would be accordingly varieddepending on different areas the pixels belong to.

A gain signal S₂ is input to the first multiplier 109 for determiningthe gain for the sharpening processing performed by the video signalprocessing device 100. The first multiplier 109 multiplies the weighingsignal S₁ by the gain signal S₂ to produce a total gain signal S₃.Referring to FIGS. 1 and 2D, the second multiplier 111 multiplies thetotal gain signal S₃ by the high-frequency signal S_(B) to produce apeaked signal S_(C). Meanwhile, the signal delayer 101 delays the inputvideo signal S_(A) so as to output a delayed video signal S₄ to theadder 113. Referring to FIGS. 1 and 2E, the adder 113 adds the delayedvideo signal S₄ to the peaked signal S_(C) so as to accomplish asharpening processing and produce the output video signal S_(D), whereinthe output video signal S_(D) includes a video signal S′ and the noisesn₁ and n₂, and the video signal S′ is obtained from the general videosignal S after receiving a sharpening processing performed by the videosignal processing device 100.

The sharpening processing method used by the video signal processingdevice 100 is usually termed as peaking processing method. Taking FIGS.2A and 2E as an example, in comparison with the video signal S, thepixel values in the portions of profiles/edges of the frame objectscorresponding to the video signal S′ after receiving a sharpeningprocessing are increased or depressed; therefore, the processing methodcauses light contours/dark contours appearing on the frame. FIG. 3 is alocalized-enlarged diagram of the video signal S′ of FIG. 2E. Referringto FIG. 3, the video signal S′ contains an area 12, and the pixel valuesof all the pixels corresponding to the area 12 are equal to the minimalpixel value of the frame. Assuming the output video signal S_(D) is thevideo signal able to display frames with 256 gray-levels, then theminimal pixel value would be equal to zero, while, on the other hand,the maximal minimal pixel value would be equal to 255. As a result, thepixels corresponding to the area 12 of the video signal S′ produce darkcontours during being displayed on a display.

In addition to the dark contours, the video signal processed by thevideo signal processing device 100 may also produce light contours onthe display. FIG. 4 is a timing diagram of another sharpened videosignal processed by the video signal processing device 100 of FIG. 1.Referring to FIG. 4, in addition to the area 12, the waveform of asharpened video signal further contains another area 14, wherein thepixel values of all the pixels corresponding to the area 14 are equal tothe maximal pixel value of the frame. As a result, the pixelscorresponding to the area 14 of the video signal S′ produce lightcontours during being displayed on the display.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an image processingmethod, which is able to produce a corresponding weight value accordingto the pixel difference value of each pixel of an input video signal,judge the area where the pixels are located in and further performcorresponding low-pass filtering processing, peaking processing orluminance transient improvement processing (LTI processing) on thepixels. By using the image processing method, the light contours or darkcontours of the frames are avoided after the sharpening processing.

The present invention is also directed to an image processing circuit,which is able to produce a corresponding weight value according to thepixel difference value of each pixel of an input video signal, judge thearea where the pixels are located in and further perform correspondinglow-pass filtering processing, peaking processing or LTI processing onthe pixels according to the different areas where the pixels are locatedin. In this way, high-quality frames are obtained.

The present invention provides an image processing method for processingan input video signal so as to produce an output video signal. The inputvideo signal contains pixel values of a plurality ofsequentially-inputted pixels. The image processing method produces aweighing signal and an area-identifying signal according to the pixeldifference values of the plurality of pixels of the input video signal.The weighing signal contains weight values of the pixels, thearea-identifying signal contains flag values of the pixels, and each ofthe flag values is configured to identify which of a first area, asecond area and a third area the pixel difference value of the pixelcorresponding to the flag value falls in. Besides, the image processingmethod uses a low-pass filter to perform a low-pass filtering processingon a first pixel among the pixels wherein the pixel difference value ofthe first pixel falls in the first area, so that the pixel value of afirst output pixels in the output video signal is obtained. The imageprocessing method further uses a high-pass processing circuit to performa peaking processing on a second pixel among the pixels wherein thepixel difference value of the second pixel falls in the second area, sothat the pixel value of a second output pixel in the output video signalis obtained. Moreover, the image processing method further uses atransient improvement circuit to perform an LTI processing on a thirdpixel among the pixels wherein the pixel difference value of the thirdpixel falls in the third area, so that the pixel value of a third outputpixels in the output video signal is obtained.

In an embodiment of the present invention, the first area and secondarea are partially overlapped. The image processing method furtherincludes performing the low-pass filtering processing and the peakingprocessing on those pixels among the pixels, wherein the pixeldifference values of those pixels fall in the overlapped portion of thefirst area and the second area.

In an embodiment of the present invention, the second area and thirdarea are partially overlapped. The image processing method furtherincludes performing the peaking processing and the LTI processing onthose pixels among the pixels, wherein the pixel difference values ofthose pixels fall in the overlapped portion of the second area and thethird area.

In an embodiment of the present invention, the second area has a firstsub-area, a second sub-area and a third sub-area. The second sub-area islocated between the first sub-area and the third sub-area. The weightvalues of the pixels corresponding to the second sub-area are greaterthan the weight values of the pixels corresponding to the first sub-areaand the third sub-area.

In an embodiment of the present invention, the weight values of thepixels corresponding to the first area and third area are equal to zero.

In an embodiment of the present invention, the high-pass processingcircuit includes a high-pass filter to perform a high-pass filteringprocessing on the input video signal so as to produce a high-passfiltered video signal.

In an embodiment of the present invention, the high-pass processingcircuit further includes a noise coring circuit coupled to the high-passfilter for removing a core component of the high-pass filtered videosignal so as to form a decored video signal.

In an embodiment of the present invention, the image processing methodfurther includes using a first multiplier to multiply the weighingsignal by a gain so as to produce a gain signal, and using a secondmultiplier to multiply the gain signal by the decored video signal so asto produce a peaked signal.

In an embodiment of the present invention, the image processing methodfurther includes using the low-pass filter to perform the low-passfiltering processing on the input video signal so as to produce alow-pass filtered video signal, and using an adder to add the low-passfiltered video signal to the peaked signal so as to produce a sharpenedvideo signal.

In an embodiment of the present invention, the image processing methodfurther includes using a delayer to delay the input video signal so asto produce a delayed video signal, and using an adder to add the delayedvideo signal to the peaked signal so as to produce a sharpened videosignal.

The present invention also provides an image processing circuit forprocessing an input video signal so as to produce an output videosignal. The input video signal contains pixel values of a plurality ofpixels sequentially input. The image processing circuit includes adifference value adaptor, a low-pass filter, a high-pass processingcircuit and a transient improvement circuit. The difference valueadaptor is configured to produce a weighing signal and anarea-identifying signal according to the pixel difference values of aplurality of pixels of the input video signal. The weighing signalcontains weight values of the pixels and the area-identifying signalcontains flag values of the pixels. Each of the flag value is configuredto identify which of a first area, a second area and a third area thepixel difference value of the pixel corresponding to the flag valuefalls in. The low-pass filter is configured to perform a low-passfiltering processing on a first pixel having the pixel difference valuefalling in the first area among the pixels so as to obtain the pixelvalue of a first output pixel of the output video signal. The high-passprocessing circuit is configured to perform a peaking processing on asecond pixel having the pixel difference value falling in the secondarea among the pixels so as to obtain the pixel value of a second outputpixel of the output video signal. The transient improvement circuit isconfigured to perform an LTI processing on a third pixel having thepixel difference value falling in the third area among the pixels so asto obtain the pixel value of a third output pixel of the output videosignal.

In an embodiment of the present invention, the first area and secondarea are partially overlapped. The low-pass filter and high-passprocessing circuit respectively perform the low-pass filteringprocessing and the peaking processing on the pixels with the pixeldifference values falling in the overlapped portion of the first areaand the second area among the pixels.

In an embodiment of the present invention, the second area and thirdarea are partially overlapped. The high-pass filter and transientimprovement circuit respectively perform the peaking processing and theLTI processing on the pixels with the pixel difference values falling inthe overlapped portion of the second area and the third area among thepixels.

In an embodiment of the present invention, the second area has a firstsub-area, a second sub-area and a third sub-area. The second sub-area islocated between the first sub-area and the third sub-area. The weightvalues of the pixels corresponding to the second sub-area are greaterthan the weight values of the pixels corresponding to the first sub-areaand the third sub-area.

In an embodiment of the present invention, the weight values of thepixels corresponding to the first area and third area are equal to zero.

In an embodiment of the present invention, the high-pass processingcircuit includes a high-pass filter to perform a high-pass filteringprocessing on the input video signal so as to produce a high-passfiltered video signal.

In an embodiment of the present invention, the image processing circuitfurther includes a first multiplier for multiplying the weighing signalby a gain so as to produce a gain signal, wherein the high-passprocessing circuit further includes: a noise coring circuit and a secondmultiplier; the noise coring circuit is coupled to the high-pass filterand is configured to remove a core component of the high-pass filteredvideo signal so as to form a decored video signal; a second multiplieris configured to multiply the gain signal by the decored video signal soas to produce a peaked signal.

In an embodiment of the present invention, the image processing circuitfurther includes a delayer and a first multiplexer. The delayer isconfigured to delay the input video signal so as to produce a delayedvideo signal, and the low-pass filter performs a low-pass filteringprocessing on the input video signal so as to produce a low-passfiltered video signal. The first multiplexer is configured to select oneof the delayed video signal and the low-pass filtered video signal foroutputting, and the high-pass processing circuit further includes anadder for adding the output of the first multiplexer to the peakedsignal so as to produce a sharpened video signal.

In an embodiment of the present invention, the image processing circuitfurther includes a second multiplexer. The second multiplexer has threeinput terminals respectively coupled to the low-pass filter, high-passprocessing circuit and transient improvement circuit. The secondmultiplexer selects corresponding pixels from the output of the low-passfilter, the output of the high-pass processing circuit and the output ofthe transient improvement circuit according to the area-identifyingsignal so as to produce the output video signal.

In an embodiment of the present invention, the image processing circuitfurther includes a second multiplexer. The second multiplexer has twoinput terminals respectively coupled to the low-pass filter and thehigh-pass processing circuit, and the output terminal of the secondmultiplexer is coupled to the transient improvement circuit. The secondmultiplexer selects corresponding pixels from the output of the low-passfilter and the output of the high-pass processing circuit according tothe area-identifying signal and sends the selected pixels to thetransient improvement circuit. The image processing circuit controls thetransient improvement circuit according to the area-identifying signaland decides whether or not to perform the LTI processing on the outputof the second multiplexer, and the output of the transient improvementcircuit is just the output video signal.

Based on the description above, the present invention is able to selectan appropriate processing to process each pixel of the input videosignal according to the pixel difference value of the pixel, wherein theprocessing includes low-pass filtering processing, peaking processing,and LTI processing. On pixels with lower pixel difference values, thelow-pass filtering processing is performed so that the correspondingarea within a frame look more smooth; on pixels with higher pixeldifference values, the LTI processing is performed so that no lightcontours and dark contours appear in the corresponding area within aframe. On pixels with moderate pixel difference values, the peakingprocessing is performed so that the profiles and the edges of the imageobjects in the corresponding area within a frame are more clear. Inaddition, the corresponding weight values of a sharpening processing areadaptively defined according to different pixel difference values, sothat the frame after the sharpening processing looks more clear andnatural.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a function block diagram of a conventional video signalprocessing device.

FIGS. 2A-2E are timing charts of the partial signals in the video signalprocessing device of FIG. 1.

FIG. 3 is a localized-enlarged diagram of the video signal S′ of FIG.2E.

FIG. 4 is a timing diagram of another sharpened video signal processedby the video signal processing device of FIG. 1.

FIG. 5 is a function block diagram of an image processing circuitaccording to an embodiment of the present invention.

FIG. 6 is a diagram showing partial pixels of an input video signalaccording to an embodiment of the present invention.

FIG. 7 is a chart showing the relationship between the pixel differencevalue and the weight value in an embodiment of the present invention.

FIG. 8 is a chart showing a partial waveform of an input video signaland the partial waveform of the corresponding output video signalproduced by the input video signal after receiving a high-pass filteringprocessing.

FIG. 9 is a chart showing a partial waveform of an input video signaland the partial waveform of the corresponding output video signalproduced by the input video signal after receiving a low-pass filteringprocessing.

FIG. 10 is a chart showing a partial waveform of an input video signaland the partial waveform of the corresponding output video signalproduced by the input video signal after receiving a transientimprovement circuit's processing.

FIGS. 11-13 are charts showing the relationships between the pixeldifference values and the weight values in different embodiments of thepresent invention.

FIG. 14 is a function block diagram of an image processing circuitaccording to another embodiment of the present invention.

FIG. 15 is a partial timing diagram of a high-pass filtered video signalaccording to an embodiment of the present invention.

FIG. 16 is a partial timing diagram of a decored video signal producedby a high-pass filtered video signal after receiving a noise coringcircuit's processing.

FIG. 17 is a function block diagram of an image processing circuitaccording to further another embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numbers areused in the drawings and the description to refer to the same or likeparts.

FIG. 5 is a function block diagram of an image processing circuit 200according to an embodiment of the present invention. Referring to FIG.5, the image processing circuit 200 receives and processes an inputvideo signal S_(IN) so as to produce an output video signal S_(OUT). Theinput video signal S_(IN) carries the information of pixel values of aplurality of pixels used for a display to display a corresponding frame.The pixel values carried by the input video signal S_(IN) aresequentially input to the image processing circuit 200. FIG. 6 is adiagram showing partial pixels of an input video signal S_(IN) accordingto an embodiment of the present invention. Referring to FIG. 6, thepixel values of a plurality of pixels P_(N−3)P_(N+3), P_(M−2)P_(M−1) andP_(M+1)-P_(M+2) are carried in the input video signal S_(IN), whereinthe pixel P_(N) is the pixel presently processed by the image processingcircuit 200, the pixels P_(M−2)-P_(M−1) and the pixels P_(M+1)-P_(M+2)are located on a same column as the P_(N), and the pixelsP_(N−3)-P_(N−1) and the pixels P_(N+1)-P_(N+3) are located on a same rowas the P_(N). The pixel values of the plurality of pixels carried by theinput video signal S_(IN) would be sequentially input to the imageprocessing circuit 200. Taking the pixels P_(N+1)-P_(N+3) as an example,the pixel values of the P_(N−3), P_(N−2), P_(N−1), P_(N), P_(N+1),P_(N+2) and P_(N+3) would be sequentially input to the image processingcircuit 200. In comparison with the input video signal S_(IN) whichcarries the information of pixel values of a plurality of pixels, theoutput video signal S_(OUT) produced by the image processing circuit 200after accomplishing the processing on the input video signal S_(IN)carries the information of pixel values of a plurality of pixels aswell. Besides, the information of pixel value of any one pixel carriedby the output video signal S_(OUT) is obtained by the image processingcircuit 200 after processing the corresponding pixel in the input videosignal S_(IN). In the embodiment, the pixel value is the luminance valueof the pixel, which the present invention is not limited to.

The image processing circuit 200 has a difference value adaptor 210,which calculates the weight value corresponding to each pixel in theinput video signal S_(IN) so as to output a weighing signal S_(W). Inthe embodiment, during calculating the weight values of pixels, thedifference value adaptor 210 defines a window 600 as shown in FIG. 6.The window 600 contains the presently processed pixel P_(N) and thepixels P_(N−2), P_(N−1), P_(N+1) and P_(N+2) all which are adjacent tothe pixel P_(N). In other words, in the embodiment, the window 600contains the presently processed pixel P_(N) and other four pixelsadjacent to the pixel P_(N). However, the number of the pixels in thewindow 600 is not limited to the above-mentioned quantity. For example,in other embodiments of the present invention, the window 600 cancontain the pixels P_(N−3)-P_(N−3), the pixels P_(N−1)-P_(N+1) or otherpixels. In addition, in the embodiment, the pixels contained by thewindow 600 are the pixels on a same pixel row in a frame, which thepresent invention is not limited to. For example, in another embodimentof the present invention, the window 600 can contain the presentlyprocessed pixel P_(N) and other pixels located on a same column as P_(N)(for example, the pixels P_(M−2), P_(M−1), P_(M+1) and P_(M+2).

Prior to calculating each weight value by the difference value adaptor210, the difference value adaptor 210 would calculate the pixeldifference value of the corresponding pixel first. Taking the pixelP_(N) in FIG. 6 as an example, when the difference value adaptor 210calculates the weight value of the pixel P_(N), the difference valueadaptor 210 would first calculate the pixel difference value D_(N)corresponding to the pixel P_(N) according to the pixel values of thepixels P_(N−2)P_(N+2) in the window 600. In the embodiment, the pixeldifference value D_(N) is equal to the result of subtracting the minimalvalue among the pixel values of the pixels P_(N−2)-P_(N+2) from themaximal value among the pixel values of the pixels P_(N−2)-P_(N+2). As aresult, the pixel difference value D_(N) can be expressed by:

D _(N) =V _(max) −V _(min)

wherein V_(max) is the maximal value among the pixel values of all thepixels in the window 600 and V_(min) is the minimal value among thepixel values of all the pixels in the window 600.

It should be noted that the calculation way of the pixel differencevalue of each pixel is not limited to the description above. Forexample, in another embodiment of the present invention, the pixeldifference value D_(N) can be expressed by:

D _(N) =|V _(N+2) V−V _(N−2) |+|V _(N+1) −V _(N−1)|

wherein V_(N+2), V_(N+1), V_(N−1) and V_(N−2) respectively denote thepixel values of the pixels P_(N+2), P_(N+1), P_(N−1) and P_(N−2) in thewindow 600.

After the difference value adaptor 210 calculates the pixel differencevalues of the pixels, the weight values of the pixels are outputaccording to the pixel values, wherein the data of the weight value ofeach pixel output by the difference value adaptor 210 is carried in theweighing signal S_(W). FIG. 7 is a chart showing the relationshipbetween the pixel difference value and the weight value in an embodimentof the present invention. Referring to FIG. 7, when the pixel differencevalue of a pixel is less than a threshold Th1 or is between a thresholdTh4 and a threshold Th5, the weight value of the pixel is equal to zero;when the pixel difference value of a pixel is between a threshold Th2and a threshold Th3, the weight value of the pixel is equal to one; whenthe pixel difference value of a pixel is between the threshold Th1 andthe threshold Th2 or between the threshold Th3 and the threshold Th4,the weight value of the pixel is between zero and one.

Continuing to FIG. 5, the image processing circuit 200 has also ahigh-pass processing circuit 220 for performing a peaking processing onthe input video signal S_(IN) according to the weight values carried bythe weighing signal S_(W). When the high-pass processing circuit 220performs the above-mentioned peaking processing, the peaking extent ofeach pixel is somewhat different depending on the corresponding weightvalue. In more details, the peaking extent for each pixel after thepeaking processing is proportional to the corresponding weight value.Besides, as the description above, the weight value of a pixel isrelated to the pixel difference value thereof, so that the peakingextent of each pixel is related to the pixel difference value thereof aswell. FIG. 8 is a chart showing a partial waveform of an input videosignal S_(IN) and the partial waveform of the corresponding output videosignal S_(OUT) produced by the input video signal S_(IN) after receivinga processing performed by the high-pass processing circuit 220.Referring to FIG. 8, the amplitudes of the input video signal S_(IN) arepositively related to the pixel values of the pixels; i.e., the largerthe amplitude of the input video signal S_(IN), the larger thecorresponding pixel value is. On the contrary, the smaller the amplitudeof the input video signal S_(IN), the smaller the corresponding pixelvalue is. In FIG. 8, there are three areas I, II and III can be roughlydistinguished from each other. The pixel values of the pixelscorresponding to the areas I and II have smaller variations, but thepixel values of the pixels corresponding to the areas III have largervariations. In this case, the high-pass processing circuit 220 woulddecreases the amplitudes of the input video signal S_(IN) located at theboundary between the areas I and II and increases the amplitudes of theinput video signal S_(IN) located at the boundary between the areas IIand III so as to produce a corresponding output video signal S_(OUT)after the peaking processing, and FIG. 8 shows the partial waveform ofthe output video signal S_(OUT).

Referring to FIG. 5 again, the image processing circuit 200 further hasa low-pass filter 230 for performing a low-pass filtering processing ona part of or all the pixels of the input video signal S_(IN). FIG. 9 isa chart showing a partial waveform S_(IN) of an input video signal andthe partial waveform of the corresponding output video signal S_(OUT)produced by the input video signal S_(IN) after receiving a processingby the low-pass filter 230. Referring to FIG. 9, when the low-passfilter 230 performs the low-pass filtering processing on the input videosignal S_(IN), the information of the high-frequency components in theinput video signal S_(IN) is filtered out, but the information of thelow-frequency components is left. In other words, the information of thepixel values carried by the input video signal S_(IN) is averaged, sothat the waveform of the output video signal S_(OUT) is smoother thanthe waveform of the input video signal S_(IN).

Continuing to FIG. 5, the image processing circuit 200 further has atransient improvement circuit 240 for performing an LTI processing on apart of or all the pixels of the input video signal S_(IN). FIG. 10 is achart showing a partial waveform of an input video signal S_(IN) and thepartial waveform of the corresponding output video signal S_(OUT)produced by the input video signal S_(IN) after receiving a processingof the transient improvement circuit 240. Referring to FIG. 10, when thetransient improvement circuit 240 performs the LTI processing on theinput video signal S_(IN), the transient of the input video signalS_(IN) within the amplitude-varied area would be shortened. In FIG. 10,there are three areas I, II and III can be roughly distinguished fromeach other. The pixel values of the pixels corresponding to the areas Iand III have smaller variations, but the pixel values of the pixelscorresponding to the areas II have larger variations. When the transientimprovement circuit 240 performs the LTI processing, the duration(width) of the area II is shortened from W1 to W2, while the height ofthe area II is still kept to H. Due to the shortened width of the areaII, the difference between the area I and the area III is more easilynoticed in terms of visual effect, which leads to sharpening the images.

Referring to FIGS. 5 and 7, in addition to outputting the weighingsignal S_(W), the difference value adaptor 210 outputs anarea-identifying signal S_(F) as well, wherein the area-identifyingsignal S_(F) has the flag values of the pixels and each flag value isused to identify which area among an first area 702, an second area 704and an area 706 the pixel difference value of the pixel corresponding tothe flag value falls in. The image processing circuit 200 controls thehigh-pass processing circuit 220, the low-pass filter 230 and thetransient improvement circuit 240 to perform the correspondingprocessing on the input video signal S_(IN) so as to produce the pixelvalue of the corresponding pixel of the output video signal S_(OUT)according to the area-identifying signal S_(F). In more details, thelow-pass filter 230 performs the low-pass filtering processing on thepixels with the pixel difference values falling in the first area 702(or termed as first pixels) so as to obtain the pixel values of firstoutput pixels in the output video signal S_(OUT); the high-passprocessing circuit 220 performs the high-pass filtering processing onthe pixels with the pixel difference values falling in the second area704 (or termed as second pixels) so as to obtain the pixel values ofsecond output pixels in the output video signal S_(OUT); the transientimprovement circuit 240 performs the LTI processing on the pixels withthe pixel difference values falling in the third area 706 (or termed asthird pixels) so as to obtain the pixel values of third output pixels inthe output video signal S_(OUT).

Referring to FIGS. 7 and 10, as the description above, when the inputvideo signal S_(IN) only receives the LTI processing performed by thetransient improvement circuit 240, the height of the area II in theproduced output video signal S_(OUT) is still kept to H. The pixelsprocessed by the transient improvement circuit 240 are the ones with thepixel difference values falling in the third area 706, and the pixeldifference values of the pixels corresponding to the third area 706 aregreater than the pixel difference values of the pixels corresponding tothe first area 702 and the second area 704. As a result, for the pixelswith larger pixel values in the input video signal S_(IN), the maximalpixel value and the minimal pixel value thereof keep unchanged, whichmakes the displaying areas corresponding to the third area 706 in aframe have no light contours and dark contours.

As shown by FIG. 7, the second area 704 has a first sub-area 711, asecond sub-area 712 and a third sub-area 713, wherein the secondsub-area 712 is located between the first sub-area 711 and the thirdsub-area 713. The weight values of the pixels corresponding to thesecond sub-area 712 are greater than the weight values of the pixelscorresponding to the first sub-area 711 and the third sub-area 713. Inaddition, the first area 702 and the second area 704 are partiallyoverlapped within the first sub-area 711, and the second area 704 andthe third area 706 are partially overlapped within the third sub-area713. The pixels with the pixel difference values falling in the firstsub-area 711 would receive the low-pass filtering processing and thepeaking processing, while the pixels with the pixel difference valuesfalling in the third sub-area 713 would receive the peaking processingand the LTI processing.

In the embodiment, the second area 704 is respectively partiallyoverlapped with the first area 702 and with the third area 706, whichthe present invention is not limited to. FIGS. 11-13 are charts showingthe relationships between the pixel difference values and the weightvalues in different embodiments of the present invention. Referring toFIGS. 11-13, in the embodiment corresponding to FIG. 11, the first area702 and the second area 704 are not overlapped, but the third area 706is partially overlapped with the second area 704. In the embodimentcorresponding to FIG. 12, the first area 702 and the second area 704 arepartially overlapped, but the third area 706 and the second area 704 arenot overlapped. In the embodiment corresponding to FIG. 13, both thefirst area 702 and the third area 706 are not overlapped with the secondarea 704. In addition, in the embodiment corresponding to FIG. 13, theweight values of the pixels corresponding to the first area 702 and thethird area 706 are equal to zero.

FIG. 14 is a function block diagram of an image processing circuit 300according to another embodiment of the present invention. Referring toFIG. 14, the image processing circuit 300 has a difference value adaptor210, a high-pass processing circuit 220, a low-pass filter 230 and atransient improvement circuit 240. The parts 210, 220, 230 and 240 havethe same functions as descriptions above, and the functions thereof areomitted to describe.

The high-pass processing circuit 220 of the image processing circuit 300has a high-pass filter 310 and a noise coring circuit 320. The high-passfilter 310 performs a high-pass filtering processing on the input videosignal S_(IN) so as to produce a high-pass filtered video signal S_(HP).The noise coring circuit 320 is coupled to the high-pass filter 310 forremoving the core component of the high-pass filtered video signalS_(HP) so as to form a decored video signal S_(C). FIG. 15 is a partialtiming diagram of a high-pass filtered video signal S_(HP) according toan embodiment of the present invention and FIG. 16 is a partial timingdiagram of a decored video signal S_(C) produced by the high-passfiltered video signal S_(HP) after receiving the processing performed bythe noise coring circuit 320. Referring to FIGS. 15 and 16, the noisecoring circuit 320 would define the core component 410 of the high-passfiltered video signal S_(HP) between a threshold T and another threshold−T. As shown by FIG. 16, after the noise coring circuit 320 removes thecore component 410 of the high-pass filtered video signal S_(HP), adecored video signal S_(C) is produced.

Referring to FIG. 14 again, the low-pass filter 230 of the imageprocessing circuit 300 performs the low-pass filtering processing on theinput video signal S_(IN) so as to produce a low-pass filtered videosignal S_(LP). The image processing circuit 300 further has a delayer250 and a first multiplexer 370. The delayer 250 delays the input videosignal S_(IN) so as to produce a delayed video signal S_(d). The firstmultiplexer 370 selects one of the low-pass filtered video signal S_(LP)and delayed video signal S_(d) for output according to the controlsignal S_(S), wherein the control signal S_(S) is produced by thedifference value adaptor 210 according to the pixel difference values.In an embodiment of the present invention, the control signal S_(S) canbe the area-identifying signal S_(F), and the first multiplexer 370selects one of the low-pass filtered video signal S_(LP) and delayedvideo signal S_(d) for output according to the area-identifying signalS_(F).

It should be noted that the overlapping of the first area 702 and thesecond area 704 in FIGS. 12 and 13 can be affected according to thedifferent definitions of the first area and the second area. Forexample, in an embodiment of the present invention, when the pixeldifference value of a pixel is less than the threshold Th1, the firstmultiplexer 370 would select the low-pass filtered video signal S_(LP)for output; when the pixel difference value of a pixel is greater thanor equal to the threshold Th1, the first multiplexer 370 would selectthe delayed video signal S_(d) for output, where the first area 702 andthe second area 704 are not overlapped, as shown by FIG. 13. In anotherembodiment of the present invention, when the pixel difference value ofa pixel is less than the threshold Th2, the first multiplexer 370 wouldselect the low-pass filtered video signal S_(LP) for output; when thepixel difference value of a pixel is greater than or equal to thethreshold Th2, the first multiplexer 370 would select the delayed videosignal S_(d) for output, where the first area 702 and the second area704 are overlapped, as shown by FIG. 14.

The image processing circuit 300 has also a first multiplier 340, whichmultiplies the weighing signal S_(W) by a gain S_(G) so as to produce again signal S_(E). In the embodiment, the gain S_(G) is used to specifyan overall gain for the high-pass processing circuit 220 to perform thepeaking processing. Usually, the gain S_(G) is adjustable. In this way,the peaking processing performed by the high-pass processing circuit 220can be flexibly adjusted to meet different application requirements.

The high-pass processing circuit 220 has also a second multiplier 350and an adder 360. The second multiplier 350 multiplies the gain signalS_(E) by the decored video signal S_(C) so as to produce a peaked signalS_(P), wherein the peaked signal S_(P) contains the high-frequencyinformation of the input video signal S_(IN). The adder 360 adds thepeaked signal S_(P) to the output of the first multiplexer 370 so as toproduce a sharpened video signal S_(SH).

In addition, the transient improvement circuit 240 performs the LTIprocessing on the input video signal S_(IN) so as to produce an LTIvideo signal S_(LTI). The image processing circuit 300 further has asecond multiplexer 380, which can select one of the sharpened videosignal S_(SH), low-pass filtered video signal S_(LP) and LTI videosignal S_(LTI) for output according to the area-identifying signalS_(F). Referring to FIGS. 12-14, when the pixel difference value of apixel is less than the threshold Th1, the second multiplexer 380 wouldselect the low-pass filtered video signal S_(LP) for output; when thepixel difference value of a pixel is between the threshold Th1 and thethreshold Th4, the second multiplexer 380 would select the sharpenedvideo signal S_(SH) for output; when the pixel difference value of apixel is greater than the threshold Th4, the second multiplexer 380would select the LTI video signal S_(LTI) for output.

FIG. 17 is a function block diagram of an image processing circuit 400according to further another embodiment of the present invention.Referring to FIG. 17, the image processing circuit 400 is similar to theimage processing circuit 300, but the major difference of the imageprocessing circuit 400 from the image processing circuit 300 rests inthat the transient improvement circuit 240 of the image processingcircuit 400 is coupled to the output terminal of the second multiplexer380, and the second multiplexer 380 of the image processing circuit 400selects one of the sharpened video signal S_(SH) and low-pass filteredvideo signal S_(LP) for output according to the area-identifying signalS_(F). For the other components of the image processing circuit 400, forexample, the difference value adaptor 210, the high-pass processingcircuit 220, the delayer 250, the low-pass filter 230 and so on, thefunctions thereof are the same as that of the image processing circuit300, so that they are omitted to describe.

In the embodiment, the image processing circuit 400 controls the secondmultiplexer 380 and selects one of the sharpened video signal S_(SH) andlow-pass filtered video signal S_(LF) for output according to theweighing signal S_(W). On the other hand, the image processing circuit400 also controls the transient improvement circuit 240 according to thearea-identifying signal S_(F) so as to decide whether or not to performthe LTI processing on the output of the second multiplexer 380. When thetransient improvement circuit 240 does not perform the LTI processing onthe output of the second multiplexer 380, the output signal of thetransient improvement circuit 240 is just the output signal of thesecond multiplexer 380.

Referring to FIGS. 17, 7 and 11-13, when the pixel difference value of apixel is less than the threshold Th1, the second multiplexer 380 wouldselect the low-pass filtered video signal S_(LP) for output; when thepixel difference value of a pixel is greater than the threshold Th1, thesecond multiplexer 380 would select the sharpened video signal S_(SH)for output.

In the embodiments corresponding to FIGS. 7 and 11, when the pixeldifference value of a pixel is greater than the threshold Th3, thetransient improvement circuit 240 would perform the LTI processing onthe output of the second multiplexer 380; when the pixel differencevalue of a pixel is less than or equal to the threshold Th3, thetransient improvement circuit 240 would not perform the LTI processingon the output of the second multiplexer 380.

In the embodiments corresponding to FIGS. 12 and 13, when the pixeldifference value of a pixel is greater than the threshold Th4, thetransient improvement circuit 240 would perform the LTI processing onthe output of the second multiplexer 380; when the pixel differencevalue of a pixel is less than or equal to the threshold Th4, thetransient improvement circuit 240 would not perform the LTI processingon the output of the second multiplexer 380.

In summary, the present invention can select an appropriate processingto process each pixel of the input video signal according to the pixeldifference value of the pixel. The processing way includes low-passfiltering processing, peaking processing and LTI processing. On pixelswith smaller pixel difference values, the low-pass filtering processingis performed, so that the corresponding areas in a frame look smoother.On pixels with larger pixel difference values, the LTI processing isperformed, so that within the corresponding areas in a frame, there areno light contours and dark contours. On pixels with modest pixeldifference values, the peaking processing is performed, so that theprofiles and the edges within the corresponding areas in a frame lookclearer. In addition, the weight value corresponding to the peakingprocessing can be adaptively set according to different pixel differencevalues, so that the frame after the peaking processing looks clearer andneutral.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncovers modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. An image processing method, for processing an input video signal soas to produce an output video signal, the input video signal containingpixel values of a plurality of pixels; the input video signalcomprising: producing a weighing signal and an area-identifying signalaccording to pixel difference values of the plurality of pixels of theinput video signal, wherein the weighing signal contains weight valuesof the pixels, the area-identifying signal contains flag values of thepixels, and each of the flag values is configured to identify which of afirst area, a second area and a third area the pixel difference value ofthe pixel corresponding to the flag value falls in; utilizing a low passfilter to perform a low-pass filtering processing on a first pixel amongthe pixels, wherein the pixel difference value of the first pixel fallsin the first area, so that the pixel value of a first output pixel inthe output video signal is obtained; utilizing a high-pass processingcircuit to perform peaking processing on a second pixel among thepixels, wherein the pixel difference value of the second pixel falls inthe second area, so that the pixel value of a second output pixel in theoutput video signal is obtained; and utilizing a transient improvementcircuit to perform luminance transient improvement (LTI) processing on athird pixel among the pixels, wherein the pixel difference value of thethird pixel falls in the third area, so that the pixel value of a thirdoutput pixel in the output video signal is obtained.
 2. The imageprocessing method as claimed in claim 1, wherein the first area and thesecond area are partially overlapped, and the image processing methodfurther comprises: performing the low-pass filtering processing and thepeaking processing on those pixels among the pixels, wherein the pixeldifference values of those pixels fall in the overlapped portion of thefirst area and the second area.
 3. The image processing method asclaimed in claim 1, wherein the second area and third area are partiallyoverlapped, and the image processing method further comprises:performing the peaking processing and the luminance transientimprovement processing on those pixels among the pixels, wherein thepixel difference values of those pixels fall in the overlapped portionof the second area and the third area.
 4. The image processing method asclaimed in claim 1, wherein the second area has a first sub-area, asecond sub-area and a third sub-area, the second sub-area is locatedbetween the first sub-area and the third sub-area, and the weight valuesof the pixels corresponding to the second sub-area are greater than theweight values of the pixels corresponding to the first sub-area and thethird sub-area.
 5. The image processing method as claimed in claim 1,wherein the weight values of the pixels corresponding to the first areaand third area are equal to zero.
 6. The image processing method asclaimed in claim 1, wherein the high-pass processing circuit comprises ahigh-pass filter to perform high-pass filtering processing on the inputvideo signal so as to produce a high-pass filtered video signal.
 7. Theimage processing method as claimed in claim 6, wherein the high-passprocessing circuit further comprises a noise coring circuit coupled tothe high-pass filter for removing a core component of the high-passfiltered video signal so as to form a decored video signal.
 8. The imageprocessing method as claimed in claim 7, further comprising: multiplyingthe weighing signal by a gain by using a first multiplier so as toproduce a gain signal; and multiplying the gain signal by the decoredvideo signal by using a second multiplier so as to produce a peakedsignal.
 9. The image processing method as claimed in claim 8, furthercomprising: performing the low-pass filtering processing on the inputvideo signal to produce a low-pass filtered video signal; and utilizingan adder to add the low-pass filtered video signal to the peaked signalso as to produce a sharpened video signal.
 10. The image processingmethod as claimed in claim 8, further comprising: delaying the inputvideo signal so as to produce a delayed video signal; and adding thedelayed video signal to the peaked signal so as to produce a sharpenedvideo signal.
 11. An image processing circuit, for processing an inputvideo signal so as to produce an output video signal, wherein the inputvideo signal contains pixel values of a plurality of pixels sequentiallyinput; the image processing circuit comprising: a difference valueadaptor, for producing a weighing signal and an area-identifying signalaccording to the pixel difference values of the plurality of pixels ofthe input video signal, wherein the weighing signal contains weightvalues of the pixels and the area-identifying signal contains flagvalues of the pixels, and each of the flag value is configured toidentify which of a first area, a second area and a third area the pixeldifference value of the pixel corresponding to the flag value falls in;a low-pass filter, for performing a low-pass filtering processing on afirst pixel having the pixel difference value falling in the first areaamong the pixels so as to obtain the pixel value of a first output pixelof the output video signal; a high-pass processing circuit, forperforming a peaking processing on a second pixel having the pixeldifference value falling in the second area among the pixels so as toobtain the pixel value of a second output pixel of the output videosignal; and a transient improvement circuit, for performing a luminancetransient improvement (LTI) processing on a third pixel having the pixeldifference value falling in the third area among the pixels so as toobtain the pixel value of a third output pixel of the output videosignal.
 12. The image processing circuit as claimed in claim 11, whereinthe first area and the second area are partially overlapped, and thelow-pass filter and the high-pass processing circuit respectivelyperform the low-pass filtering processing and the peaking processing onthe pixels having the pixel difference values falling in the overlappedportion of the first area and the second area among the pixels.
 13. Theimage processing circuit as claimed in claim 11, wherein the second areaand third area are partially overlapped, and the high-pass filter andthe transient improvement circuit respectively perform the peakingprocessing and the luminance transient improvement processing on thepixels having the pixel difference values falling in the overlappedportion of the second area and the third area among the pixels.
 14. Theimage processing circuit as claimed in claim 11, wherein the second areahas a first sub-area, a second sub-area and a third sub-area, the secondsub-area is located between the first sub-area and the third sub-area,and the weight values of the pixels corresponding to the second sub-areaare greater than the weight values of the pixels corresponding to thefirst sub-area and the third sub-area.
 15. The image processing circuitas claimed in claim 11, wherein the weight values of the pixelscorresponding to the first area and third area are equal to zero. 16.The image processing circuit as claimed in claim 11, wherein thehigh-pass processing circuit comprises a high-pass filter to perform ahigh-pass filtering processing on the input video signal so as toproduce a high-pass filtered video signal.
 17. The image processingcircuit as claimed in claim 16, further comprising a first multiplierfor multiplying the weighing signal by a gain so as to produce a gainsignal, wherein the high-pass processing circuit further comprises: anoise coring circuit, coupled to the high-pass filter for removing acore component of the high-pass filtered video signal so as to form adecored video signal; and a second multiplier, for multiplying the gainsignal by the decored video signal so as to produce a peaked signal. 18.The image processing circuit as claimed in claim 17, further comprisinga delayer and a first multiplexer, wherein the delayer is configured todelay the input video signal so as to produce a delayed video signal,and the low-pass filter performs the low-pass filtering processing onthe input video signal so as to produce a low-pass filtered videosignal; the first multiplexer is configured to select one of the delayedvideo signal and the low-pass filtered video signal for outputting, andthe high-pass processing circuit further comprises an adder for addingthe output of the first multiplexer to the peaked signal so as toproduce a sharpened video signal.
 19. The image processing circuit asclaimed in claim 11, further comprising a second multiplexer, whereinthe second multiplexer has three input terminals respectively coupled tothe low-pass filter, the high-pass processing circuit and the transientimprovement circuit; the second multiplexer selects corresponding pixelsfrom the output of the low-pass filter, the output of the high-passprocessing circuit and the output of the transient improvement circuitaccording to the area-identifying signal so as to produce the outputvideo signal.
 20. The image processing circuit as claimed in claim 11,further comprising a second multiplexer having two input terminals andan output terminal, wherein the two input terminals are respectivelycoupled to the low-pass filter and the high-pass processing circuit, theoutput terminal is coupled to the transient improvement circuit, thesecond multiplexer selects corresponding pixels from the output of thelow-pass filter and the output of the high-pass processing circuitaccording to the area-identifying signal and sends the selected pixelsto the transient improvement circuit, the image processing circuitcontrols the transient improvement circuit according to thearea-identifying signal and decides whether or not to perform theluminance transient improvement processing on the output of the secondmultiplexer, and the output of the transient improvement circuit is justthe output video signal.